1. Technical Field of the Invention
This invention relates generally to wireless communications and more particularly to accurately measuring transmits signal strength of such wireless communications.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is further known, many transmitters include a transmit signal strength indication (TSSI) module that measures the signal strength of the RF signals at the output of the power amplifier. The measured signal strength is used to adjust gain of the power amplifier, regulate a constant transmit power, and other power conserving operations. Accordingly, for such operations to be accurately performed, the measured signal strength must be accurate.
One common embodiment of a TSSI module includes a peak detector and a peak-to-power conversion module. The peak detector includes an operational amplifier having a non-inverting input, an inverting input, and an output, where the inverting input is coupled to receive the RF signals. The peak detector also includes a transistor and a capacitor. The transistor includes a gate, a drain, and a source. The gate of the transistor is coupled to the output of the operational amplifier and the drain of the transistor is coupled to the non-inverting input of the operational amplifier and to one plate of the capacitor to provide an output of the peak detector. The other plate of the capacitor is coupled to a circuit ground and the source of the transistor is coupled to a power supply voltage. As coupled, the peak detector measures peaks of the transmitted RF signals with respect to a circuit ground. The peak-to-power conversion module converts the measured peak values into a corresponding power to produce a transmit signal strength indication.
An issue arises with such a peak detector when the frequency of the transmitted RF signals enters the giga-Hertz range in that, the signal is transitioning too fast for the peak detector to accurately determine the peak value. In this instance, the peak detector provides an average value with respect to the circuit ground, which yields inaccurate transmit signal strength indications.
Therefore, a need exists for a high frequency peak detector that provides an accurate measure of peak values of high frequency signals, including radio frequency signals.